The present invention relates to fluid pumps for supplying a fluid, and more particularly, to fluid pumps that are used as fuel pumps for supplying fuel from a fuel tank to an engine.
An example of a fuel pump is disclosed in Japanese Laid-Open Patent Publication No. 8-14184, which is an in-tank fuel pump disposed within a fuel tank.
In this known fuel pump, an impeller is mounted on a shaft of a motor and is rotatably disposed within a pump housing. Blades are formed within both axial end surfaces of the impeller and are disposed at a predetermined pitch along the perimeter of the impeller. A blade groove is formed between each of the blades. The pump housing has an inlet port through which fuel flows in, an outlet port through which fuel is discharged, a pump channel and a partition. The inlet port is formed on one axial side of the impeller. The outlet port is formed on the other axial side of the impeller. The pump channel extends from the inlet port to the outlet port along a travelling path of the impeller blades. The partition is formed between the inlet port and the outlet port. The pump channel includes a first pump channel and a second pump channel. The first pump channel faces one end surface of the impeller on the side of the inlet port. The second pump channel faces the other end surface of the impeller on the side of the outlet port. In this known fuel pump, a terminal end of the outlet port is located at a position displaced by one-half of the pitch of the blades from a terminal end of the first pump channel downstream in the direction of rotation of the impeller. Further, a starting end of the second pump channel is located at a position displaced by one-half of the pitch of the blades from a starting end of the inlet port downstream in the direction of rotation of the impeller.
In fuel pumps that are typically used, one-half of the pitch of the blades is about 10xc2x0 or less. Specifically, in this case, the terminal end of the outlet port is located at a position displaced at a maximum of about 10xc2x0 from the terminal end of the first pump channel downstream in the direction of rotation of the impeller. The starting end of the second pump channel is located at a position displaced at a maximum of about 10xc2x0 from the starting end of the inlet port downstream in the direction of rotation of the impeller.
Fuel that flows through the second pump channel is directly discharged through the outlet port. Further, fuel flowing through the first pump channel is drawn from near the terminal end of the first pump channel to the second pump channel and then discharged through the outlet port. In the known fuel pump, if the rotational speed (peripheral velocity) of the impeller is high, fuel flowing through the first pump channel will pass a position corresponding to the outlet port before flowing from near the terminal end of the first pump channel to the second pump channel. Therefore, the known fuel pump cannot increase fuel discharge, thus preventing an increase in the pump efficiency.
Further, some of the fuel within the blade grooves is not discharged through the outlet port. Such fuel is drawn toward the inlet port while being confined within the blade grooves by the partitions. The fuel that is confined within the blade grooves by the partitions is highly pressurized. Therefore, after having passed along the partitions, such fuel is ejected into the second pump channel and the inlet port at the starting end of the second pump channel and the starting end of the inlet port. In the known fuel pump, the high-pressure fuel that has been confined within the blade grooves flows back into the inlet port and collides with fuel that flows in through the inlet port. Therefore, the known fuel pump cannot increase the amount of fuel that flows in through the inlet port, thus preventing an increase in the pump efficiency.
It is, accordingly, an object of the present invention to provide a fluid pump having increased pump efficiency.
One means for attaining this object is to adjust the distance between a terminal end of the outlet port and a terminal end of the first pump channel provided on the side of the inlet port. Preferably, the terminal end of the outlet port is located at a position displaced about 25xc2x0 to 60xc2x0 from the terminal end of the first pump channel in the direction of rotation of the impeller. With this construction, the fluid that flows through the first pump channel can be reliably discharged through the outlet port even when the rotational speed of the impeller is high. Thus, the pump efficiency can be increased.
Another means for attaining this object is to provide an enlarged channel portion that is defined between a partition and a channel communicating portion at which the first pump channel communicates with the inlet port. The enlarged channel portion has a larger flow passage area than a flow passage area decreased by the partition. In this case, the distance between a starting end of the second pump channel and a starting end of the enlarged channel portion is preferably adjusted. Thus, the starting end of the second pump channel is preferably located at a position displaced about 8xc2x0 to 30xc2x0 from the starting end of the enlarged channel portion in the direction of rotation of the impeller. With this construction, the high-pressure fuel that has been confined within the blade grooves can be prevented from flowing back into the inlet port. Further, negative pressure can be increased in the channel communicating portion on the side of the inlet port. Thus, the amount of fluid that flows in through the inlet port can be increased, thereby improving the pump efficiency.
A further means for attaining this object is to adjust the length of the partition formed on the side of the second pump channel. Preferably, the angular length of the partition formed on the side of the second pump channel is chosen to be between about 25xc2x0 to 45xc2x0. With this construction, the relationship between the length (sealing width) of the partition and the flow passage length of the second pump channel can be optimized, so that the pump efficiency can be increased.
A still further means for attaining this object is to adjust the length of the partition formed on the side of the first pump channel. Preferably, the angular length of the partition formed on the side of the first pump channel is chosen to be between about 60xc2x0 to 80xc2x0. With this construction, the relationship between the length (sealing width) of the partition and the flow passage length of the first pump channel can be optimized, so that the pump efficiency can be increased.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.